1. Field of the Invention
The present invention relates to a thin-film transistor, a method of manufacturing the thin-film transistor, a display device, and an electronic apparatus.
2. Description of the Related Art
It is widely known that a thin-film transistor (TFT) is formed, as a driving device for active matrix of a liquid crystal display device, on a transparent substrate such as a glass substrate. In recent years, in order to deal with display of many varieties of information, an improvement in high-definition of pixels of a liquid crystal display device is under way. As reduction in area of each of the pixels is caused by the improvement in high-definition thereof, a sufficient opening area is secured to prevent display luminance of each of the pixels from decreasing. As a result, a decrease in an area of a portion where a charge of the pixel is held, i.e., a decrease in a storage capacity is inevitable. The decrease in the storage capacity will lead to such problem that a leak current (photo leak current) of a pixel transistor that is induced at the time when backlights illuminate has increased influence on a decrease in the charge of the pixel. Hence, the decrease in the charge of the pixel causes a fall in contrast.
In an organic electroluminescence display device, in which an organic electroluminescence device is used as a self-emitting element therefor, there is a mode in which a TFT is formed, as a driving device for active matrix of a bottom emission type, on a transparent substrate. In that case, external light that is made incident through a glass substrate will cause an increase in a photo leak current of the TFT, and thereby a fall in contrast is caused. Therefore, in such a case when the external light is made incident from the glass substrate side, a light blocking layer is formed between the TFT and the glass substrate to prevent the external light from being made incident on the TFT. In other words, there is employed such an approach for suppressing the photo leak current in which the light blocking layer is used to suppress the incidence of the external light on the TFT.
JP2001-284594A (paragraphs 0015 to 0020 on pages 2 to 3) proposes a structure for a TFT having a so-called LDD (Lightly-Doped Drain) structure, wherein low-concentration impurity regions are provided on both sides of a gate electrode, in which a light blocking film two-dimensionally covers a channel region and the low-concentration impurity regions provided on both sides of the channel region. Specifically, an amorphous silicon film, which is deposited on an upper layer of a light blocking film made of nontransparent metal, is polycrystallized by a laser beam irradiated thereon to form a polysilicon film, which is used as the channel region and the low-concentration impurity regions provided on both the sides of the channel region. In the structure, a crystal grain size in the obtained polysilicon film is large and uniform, and proposed is a suitable structure capable of suppressing leak current of the TFT when being irradiated with light.
JP2007-109868A (paragraphs 0006 to 0010 on pages 3 to 4) proposes such a TFT in which a light blocking layer is formed to cover only a boundary region of a drain region and a channel region is provided. Generation of a photo leak current in the boundary region of the drain region and the channel region, which is in a reverse bias state, is suppressed, whereby an effect of reducing fluctuation in performance (e.g., a threshold voltage) of a thin-film transistor is obtained.